Inductively back-coupled tube generator



y 29, 34- H. SCHUMACHER 1,960,419

INDUCTIVELY BACK COUPLED TUBE GENERATOR Filed Dec. 11, 1930 Patented May29, 1934 UNITED STATES PATENT OFFICE INDUCTIVELY BACK-COUPLED TUBEGENERATOR Application December 11, 1930, Serial No. 501,538 In GermanyDecember 18, 1929 1 Claim.

The present invention relates to an inductively back-coupled vacum tubeoscillation generator, the fundamental principle of which is generallyknown. A difliculty often found in generators of 5 this type consists inthat they are not able to maintain the frequency produced sufficientlyand exactly constant for all purposes. As long as one singletransmitting apparatus operates on one wave, as is commonly done inwireless telegraphy, it is not so important that the constancy of thefrequency as such be maintained as is the case when broadcasting withequal or carrier waves. If it is desired to use tube generators for thelatter purpose, arrangements must be provided, which will maintain thefrequency sufliciently constant. It has been ascertained by tests thatit is necessary in the first place to stop the grid current. Accordingto this invention no use is made of a condenser, as should be ex- 20pected on first thought, for that purpose, but

merely, of a crystal of quartz. For the transmitting tube, preferably atube with a screen grid is employed, the screen grid of which, however,has been left on an open circuit.

A preferred embodiment of the arrangement according to the invention isillustrated diagrammatically in the drawing by way of example.

Figure 1 represents diagrammatically a vacuum tube oscillation generatorof known design, being inductively back-coupled, and adapted for useaccording to this invention, and

Figure 2 shows diagrammatically a similar view. The blocking or stoppingmeans is applied according to this invention in conjunction with avariable condenser c shunting the crystal Q.

Referring to the tube generator represented in the drawing, the grid Gof the tube R is backcoupled by way of the coil L1 with the tuned coilL2. A condenser C is associated with the coil L2 for tuning purposes.The anode potential is supplied in known manner between the andterminals. Normally Q is not inserted, L1 being connected between thegrid and the terminal.

In the arrangement shown in the drawing there is a quartz crystal Qinterposed, according to the invention, in the grid circuit for thepurpose of stopping or blocking the continuous current of 0 the grid. Inspecial cases, the arrangement may be rendered more complete if acondenser c is connected in parallel with the piece of quartz Q,

as shown in Fig. 2. These arrangements of elements offer the advantageover the customary devices, in that the tube may be energized bygenerators and not, as was the ease up to the present, by batteriesonly. In addition, the minute supervision which was formerly required,

of the voltages of the batteries by means of pre- 7 cision instrumentsis rendered unnecessary. With the modified apparatus it is merelynecessary to protect the piece of quartz against changes of temperatureby means of thermostats of known construction. As this can be accom- 7plished very easily, it is obvious that the arrangement according to theinvention will offer considerable advantages.

This is usually done if the susceptance of the piece of quartz is toosmall to cause any generation of oscillations.

What is claimed is:

An oscillation generator comprising a vacuum tube having a cathode, acontrol grid, an anode and a floating screen grid interposed between thecontrol grid and the anode, a circuit connected between said cathode andsaid anode, an inductance shunted by a tuning condenser included in saidcircuit, a circuit connected between said control grid and said cathode,an inductance in said grid cathode circuit coupled to the anode circuitinductance, and a frequency determining quartz crystal connected in saidgrid cathode circuit in series with said inductance thereof so as toblock direct current from said control grid.

HANS SCHUMACHER.

